1. Field of the Invention
The invention relates to an additive combination of (a) an ethylene backbone middle distillate fuel oil pour depressant polymer with (b) a second polymer comprising an oil-soluble sulfone copolymer. This combination is particularly useful in middle distillate fuel oils containing a fraction boiling above 175.degree. C. for controlling the size of wax crystals that form at low temperatures.
2. Description of the Prior Art
Various polymers, useful as middle distillate pour point depressants, prepared from ethylene have been described in the patent literature. These pour depressants include co-polymers of ethylene and vinyl esters of lower fatty acids such as vinyl acetate (U.S. Pat. No. 3,048,479); copolymers of ethylene and alkyl acrylate (Canadian Pat. No. 676,875); terpolymers of ethylene with vinyl esters and alkyl fumarates (U.S. Pat. Nos. 3,304,261 and 3,341,309); polymers of ethylene with other lower olefins, or homopolymers of ethylene (British Pat. Nos. 848,777 and 993,744); chlorinated polyethylene (Belgium Pat. No. 707,371 and U.S. Pat. No. 3,337,313); etc.
The sulfone copolymer products resulting from the polymerization of sulfur dioxide with unsaturated compounds such as unsaturated alcohols, ethers, esters and acids are well known in the art as for example as seen from U.S. Pat. No. 2,114,292. It is also known to react sulfur dioxide with olefins and ethylenically unsaturated polar compounds as for example is seen from U.S. Pat. Nos. 2,241,900, 2,645,631, 3,563,961 and 3,684,778. These copolymers of sulfur dioxide and ethylenically unsaturated polar compounds were prepared by various processes, including bulk, solution and emulsion polymerization.
U.S. Pat. No. 2,652,368 describes the use of alkylene sulfone copolymers of SO.sub.2 and olefins in lubricating oil compositions to enhance its viscosity temperature performance in torque converters. These copolymers were obtained by the polymerization of alpha-olefinic hydrocarbons having from 7 to 24 carbon atoms with SO.sub.2 at the latter's reflux temperature and in the presence of a catalyst such as peroxides and nitrates.
U.S. Pat. No. 3,442,790 teaches olefin and sulfur dioxide copolymers as wax crystal modifiers. These materials are added to wax-containing petroleum oil materials, for example, so as to modify the size and shape of wax crystals in such a manner as to permit more rapid separation of the wax during the dewaxing of the hydrocarbon oil.